Toxocariasis is a helminth infection of human which is caused by roundworm, Toxocara canis or Toxocara cati. This infection occurs when embryonated eggs containing fully developed infective larvae of the Toxocara spp. are ingested. The larvae in the human intestine will penetrate the bowel wall and migrate through blood vessels to reach liver, muscles and lungs, even into eye and brain. Therefore, a method for diagnosis and detection of toxocariasis is crucial for its prevention and treatment.
There are hardly any patented technologies relating to the detection or diagnosis of toxocariasis in the prior arts. Most of the serological and immunological studies of nematode parasites disclosed in the prior arts are designed for the diagnosis of heartworm, such as Dirofilaria immitis as described in U.S. Pat. No. 6,103,484.
Some patented technologies aim to detect and raise antibodies against various species of nematode parasites, including the species of the genera Trichinella, Osteragia, Dirofilaria, Toxocara and others. In U.S. Pat. No. 5,948,644, an isolated polynucleotide segment comprising a nucleotide sequence encoding an excretory-secretory protein having molecular weight of 11 kDa, 17 kDa, 30 kDa, 37 kDa and 81 kDa is disclosed. Apart from that, a purified antigen derived from a parasitic nematode species having molecular weight of 40 kDa is also disclosed in U.S. Pat. No. 5,871,738. These inventions helps to provide antibodies against the antigens and related molecules, and antibody compositions comprising the antibodies, vaccines comprising the antigens and others. However, these methods are complicated and the proteins used are not specific.
Most of the patented technologies use proteins of higher molecular weight in the detection of nematode parasites. In addition, the methods disclosed are not capable of detecting or diagnosing toxocariasis specifically. Even though the excretory-secretory antigens derived from T. canis second stage infective larvae (L2) maintained in defined medium in vitro have been extensively used for the immunodiagnosis of human toxocariasis, immunoassays using serum samples from patients with ascariasis, filariasis and strongyloidiasis, however, shows cross-reactivities with the native TES.
Therefore, it is desirable for the present invention to innovate an antigen which is capable of specifically detecting toxocariasis to overcome the drawbacks of the prior arts. As low molecular weight antigens are shown to be more specific than high molecular proteins for detection of toxocariasis, a suitable protein derived from Toxocara larvae can be applied to develop a more useful and effective serodiagnostic marker for this disease.